Method and device for determining the geometric vehicle inclination of a motor vehicle

ABSTRACT

A method is for determining a geometric vehicle inclination α of a motor vehicle, where an acceleration signal of at least one acceleration sensor is used and a speed gradient dv/dt is determined from a measured vehicle speed v, where a) in the case of a moving or standing vehicle, an acceleration value a S  is derived from a force acting on the acceleration sensor, b) a corrected acceleration value a korr  is determined as a function of the speed gradient dv/dt, and c) the current vehicle inclination α is directly deduced from the corrected acceleration value a korr . In addition, a device for implementing a method to determine a geometric vehicle inclination α of a motor vehicle, the device includes a speed-measuring device and at least one acceleration sensor, a programmable and readable microcontroller being provided, with the aid of which the current vehicle inclination a may be calculated from the values of the speed-measuring device and the acceleration sensor at a vehicle speed v of the vehicle greater than or equal to zero, and directly transmitted to at least one control unit.

FIELD OF THE INVENTION

The present invention relates to a method for determining a geometricvehicle inclination α of a motor vehicle, where an acceleration signalof at least one acceleration sensor is used and a speed gradient dv/dtis calculated from a measured vehicle speed v.

The present invention also relates to a device for implementing a methodto determine a geometric vehicle inclination α of a motor vehicle, thedevice having a speed-measuring device and at least one accelerationsensor.

BACKGROUND INFORMATION

The handling and the performance of a motor vehicle is, to aconsiderable extent, a function of its current geometric inclination,i.e., if it is on a flat or an inclined roadway. For example, thecontrol of the control systems mostly available in modern motorvehicles, such as ABS (anti-lock brake system), TCS (traction controlsystem) and ESP (electronic stability program) should be adjusted to thespecific vehicle inclination. These systems are equipped withacceleration sensors and speed sensors, and, in certain drivingsituations, they intervene in the brake management and enginemanagement. Knowledge of the vehicle inclination is important foroptimally controlling the braking performance and traction performance.Knowledge of the vehicle inclination may also have an influence on or betransmitted to the transmission control system, in order to improve thegear-shifting operations and protect against unintentional switchingoperations while driving uphill and downhill. In addition, theinclination of a stationary vehicle is also of interest, e.g., forprotecting against rolling back unintentionally and optimizing thedriveaway characteristics. Furthermore, knowledge of a transverseinclination, i.e., transverse to the driving direction, is veryimportant for preventing a possible overturning hazard, especially inthe case of so-called off-road vehicles, when the roadway conditions aredifficult on pathless terrain.

In the case of conventional systems having special inclination sensors,it has turned out to be a problem that they often register incorrectinclination values in the event of simultaneous vehicle accelerations.Other systems only determine the values after a certain driving time ordriving distance or are only suitable for determining longitudinalinclinations.

A method for detecting uphill or downhill driving of a motor vehicle isdescribed in German Published Patent Application No. 100 26 102. Theobject of the method is to bring a reference speed, which is determinedfrom wheel-speed sensor signals and can significantly deviate from theactual vehicle speed in certain situations, e.g., in the case ofspinning wheels, toward the actual speed as rapidly as possible, inorder to thereby improve the control of electronic systems, which referto the reference speed. A reference acceleration is determined from thereference speed of the vehicle, using differentiation. This is comparedto a sensor-determined, longitudinal vehicle acceleration. If thedifference of the longitudinal vehicle acceleration and the referenceacceleration exceeds a specified threshold value over a certain minimumperiod of time, then uphill or downhill driving is detected.

In the conventional method, it turns out to be disadvantageous that itonly functions in the case of a moving vehicle, and that a certaindistance traveled or driving time is necessary for detecting a vehicleinclination. In addition, it is only suitable for detecting longitudinalinclinations, i.e., inclines or declines, but not for detectingtransverse inclinations. It is also disadvantageous that, in the case ofall-wheel drive vehicles, the drive or transmission must be temporarilyinterrupted at one axle, in order to implement the method. In addition,a relatively complicated, digital, logical counting circuit isnecessary.

A method for determining the longitudinal roadway inclination, one amotor vehicle is driven without braking it, is described in GermanPublished Patent Application No. 43 08 128. In this connection, a slipdifference is determined by comparing the wheel speeds of the wheels ona driven axle and a freely revolving axle. A flat roadway, an incline,or a decline is detected as a function of the combination of theslip-difference sign and the sign of a vehicle speed change determinedfrom the wheel speeds.

In the case of the conventional method, it is disadvantageous that it isonly usable while driving without braking. In addition, it is notdesigned for all-wheel-drive vehicles and is only suitable fordetermining a longitudinal inclination.

Therefore, an aspect of the present invention is to provide a method fordetermining a vehicle inclination, which may immediately provide thecurrent geometric vehicle inclination, both during vehicle operation andwhen the vehicle is stationary, which may be suitable for determininglongitudinal and transverse inclinations, and which may not require mucheffort to implement.

SUMMARY

In an example embodiment of the present invention:

-   a) in the case of a traveling or standing vehicle, an acceleration    value a_(S) is derived from a force acting on acceleration sensor 1;-   b) a corrected acceleration value a_(korr) is calculated as a    function of speed gradient dv/dt; and-   c) current vehicle inclination α is directly deduced from corrected    acceleration value a_(korr).

An available acceleration signal, e.g., a longitudinal acceleration inthe ESP, is evaluated together with a speed signal already available aswell, e.g., in the case of all vehicles equipped with ABS, such thatactual inclination α of the vehicle may be immediately available, i.e.,without the vehicle having to travel a certain distance or a certainperiod of time having to elapse during which various measurements mustbe made. Even in the case of a standing vehicle, the acceleration sensoroutputs an acceleration value corresponding to the force or mass actingon it, the force or mass being able to be produced by, e.g., a change inthe axle-load distribution on an incline in comparison with that of aflat roadway. During the drive, a falsification of the ascertainedresult due to possible speed changes of the vehicle may be prevented bytaking speed gradient dv/dt into consideration.

In an example embodiment of the present invention, vehicle inclination αmay be calculated according to the equation

$\alpha = {\arcsin{\left\{ \frac{\left( {a_{s} - {{\mathbb{d}v}/{\mathbb{d}t}}} \right)}{g} \right\}.}}$

An acceleration sensor may not distinguish or determine whether thevalue indicated by it is caused by a change in vehicle speed v or by avehicle inclination α. However, it may always indicate the suma_(s)=g·sin α+dv/dt. Since vehicle speed v is measured in all modernvehicles, a vehicle speed change dv/dt may also be derived. Therefore,geometric inclination α of the vehicle (in radians) may be directlydetermined according to the above equation, using gravitationalacceleration g=9.81 m/s². During the determination of transverseinclinations, the effects of centrifugal accelerations are additionallyconsidered in the calculation.

According to an example embodiment of the present invention, correctedacceleration value a_(korr)=a_(s)−dv/dt may be compared to a specifiedthreshold acceleration value a_(S1) of acceleration sensor 1, and adifference may be made between an incline and a decline as a function ofa deviation direction.

On the basis of, for example, a calibration, the acceleration sensor isassigned a threshold value, which corresponds to a flat roadway. Theupward or downward deviation of corrected acceleration value a_(korr)from threshold value a_(S1) allows a difference to be made between anincline and a decline. Depending on the arrangement and design of theread-out acceleration sensor, a particular deviation direction maycorrespond to an incline or a decline in the direction of travel.

According to an example embodiment of the present invention, alongitudinal inclination α_(L) of the vehicle may be determined from theacceleration signal of a longitudinal-acceleration sensor. In addition,a transverse inclination α_(Q) of the vehicle may be determined from theacceleration signal of a transverse-acceleration sensor.

The method may be suitable for determining both longitudinalinclinations, i.e., inclines or declines, and transverse inclinations,i.e., lateral roadway inclinations transverse to the direction oftravel. This information may be transmitted to the electronic controlsystems of the vehicle, which means that the information may improve thereliability of these systems and increases the safety of the vehicleperformance, in particular in limit situations.

Conventional devices for implementing methods to determine aninclination of a motor vehicle have the disadvantage that they are notdesigned for standing vehicles. In addition, they cannot determinetransverse inclinations.

Therefore, a further aspect of the present invention is to provide adevice, by which longitudinal and transverse inclinations may bedetermined for standing and moving vehicles.

In this regard, a programmable and readable microcontroller may beprovided, with the aid of which current vehicle inclination α may becalculated from the values of the speed-measuring device and theacceleration sensor at a vehicle speed v of the vehicle greater than orequal to zero, and directly transmitted to at least one control unit.

The microcontroller may be programmed with one or more computationalalgorithms, which process the speed and acceleration values and outputthe geometric vehicle inclination as a result. The microcontrollerdifferentiates between longitudinal and transverse inclination, as wellas between decline and incline, in accordance with the sensor data. Theoutputted signals are conditioned so that they may be passed on to acontrol unit for further processing.

According to an example embodiment of the present invention, the signalsoutput by the microcontroller may be processed further by a transmissioncontrol unit. The microcontroller signals may also be processed furtherby an engine control unit and/or an all-wheel-drive control unit and/ora brake control unit; and/or an adaptive cruise control unit and/or avehicle-dynamics control unit and/or a drive-train control unit. Ingeneral, the control units are operatively connected to each other andto the existing control systems, such as ABS, TCS, and ESP.

The signals of the microcontroller are conditioned so that they may beread by the control units. These data may then be used for optimizingthe gearshift-mechanism control, e.g., in automatic transmissions, andfor controlling the power output and torque output of the driving engineon inclines and declines. In the case of a standing vehicle, theinclination data may be used, for example, to activate devices forpreventing unintentional backwards-rolling. More specific and moreeffectively dosed braking actions may be undertaken by the ABS with theaid of the inclination data. The TCS functions comparably in limitsituations, e.g., with respect to the driveaway characteristics, and theESP functions comparably in limit situations, with respect to thecornering ability.

An example embodiment of the present invention provides an instrumentdisplay, on which vehicle inclination α is displayable.

The display may show the current vehicle inclination converted to anupgrade or downgrade %. This may allow the driver to receive additional,useful information, in order to possibly adapt his driving behavior tothe corresponding situation in a more effective manner.

According to an example embodiment of the present invention, a rolloverwarning device may be activated in response to a specifiable transverseinclination α_(Q).

The rollover warning may be of an acoustic or optical kind. This mayallow the driver to timely react in limit situations, which means thatthe safety may be increased, e.g., in the case of off-road vehicles.

Further details of the present invention are derived from the followingdetailed description and appended Figure, in which an example embodimentof the present invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram to illustrate the method for ascertaining ageometric vehicle inclination of a motor vehicle.

DETAILED DESCRIPTION

A device for implementing a method to determine a geometric vehicleinclination α of a motor vehicle is essentially made up of aspeed-measuring device 2, an acceleration sensor 1, and amicrocontroller 3.

Speed-measuring device 2 may include a speed sensor on each wheel. Thevehicle may include an ESP longitudinal-acceleration sensor, which formsacceleration sensor 1. Speed-measuring device 2 and acceleration sensor1 are connected via signal lines to microcontroller 3, which has, on itspart, an output unit 4. Further signal lines lead from this output unit4 to a transmission control unit 5 and an engine control unit 6. Controlunits 5, 6 are bidirectionally connected among each other so as to beable to transmit signals to each other, and they are connected to threecontrol systems 7, 8, 9. The control systems take the form of an ABScontrol system 7, a TCS control system 8, and an ESP control system 9.

A method for determining a geometric vehicle inclination α of a motorvehicle is essentially based on the evaluation of an acceleration signala_(S), while taking a speed gradient dv/dt into consideration.

Speed-measuring device 2 evaluates the individual, measured wheel speedsand determines a vehicle speed v from them, which is transmitted tomicrocontroller 3. Microcontroller 3 calculates a speed gradient dv/dt,using differentiation. Acceleration sensor 1 transmits an accelerationvalue a_(S) to microcontroller 3. A computational algorithm according tothe equation a_(korr)=a_(s)−dv/dt is programmed in microcontroller 3.

The subtracting of speed gradient dv/dt from acceleration value a_(s)yields a corrected value a_(korr) independent of vehicle speed v. Whenthe vehicle is standing, dv/dt=0 directly results in a_(S)=a_(korr).Longitudinal vehicle inclination α_(L) determined according to thelongitudinal-acceleration sensor is transmitted as a result of thealgorithm, to output unit 4, which transmits, for its part, thecorrespondingly conditioned signal to transmission control unit 5 andengine control unit 6, by which the signal is supplied, in eachinstance, to control systems 7, 8, 9. A transverse inclination α_(Q) maybe determined in an analogous manner, using a transverse-accelerationsensor. In this context, the computational algorithm is modified in viewof the centrifugal forces. In addition, microcontroller 3 may transmitdata, such as vehicle speed v, directly from speed-measuring device 2 tothe control systems. Control units 5, 6 and control systems 7, 8, 9 takespecific vehicle inclination α_(L) or α_(Q) into consideration in theirresponse, for instance in gear changes, engine-torque reductions, orbraking actions.

LIST OF REFERENCE NUMBERALS

-   1 acceleration sensor-   2 speed-measuring device-   3 microcontroller-   4 output unit-   5 transmission control unit-   6 engine control unit-   7 ABS control system-   8 TCS control system-   9 ESP control system

1. A method for determining a geometric vehicle inclination of a motorvehicle, comprising: calculating a speed gradient from a measuredvehicle speed; deriving an acceleration value from a force acting on anacceleration sensor for one of (a) a traveling vehicle and (b) astanding vehicle, the acceleration sensor configured to generate anacceleration signal; calculating a corrected acceleration value as afunction of the speed gradient; directly calculating a current vehicleinclination from the corrected acceleration value; comparing thecorrected acceleration value to a predetermined threshold accelerationvalue of the acceleration sensor; and determining one of (a) an inclineand (b) a decline as a function of a deviation direction.
 2. The methodaccording to claim 1, wherein the vehicle inclination is calculated inthe vehicle inclination calculating step according to the equation:${\alpha = {\arcsin\left\{ \frac{\left( {a_{s} - {{\mathbb{d}v}/{\mathbb{d}t}}} \right)}{g} \right\}}};$wherein a represents the vehicle inclination, a_(s) represents theacceleration value, and dv/dt represents the speed gradient.
 3. Themethod according to claim 1, wherein the corrected acceleration valuesatisfies the relationship a_(korr)=a_(s)−dv/dt; wherein a_(korr)represents the corrected acceleration value, a_(s) represents theacceleration value, and dv/dt represents the speed gradient.
 4. Themethod according to claim 1, further comprising determining alongitudinal inclination of the vehicle from an acceleration signal of alongitudinal-acceleration sensor.
 5. The method according to claim 1,further comprising determining a transverse acceleration of the vehiclefrom an acceleration signal of a transverse-acceleration sensor and acentrifugal acceleration.
 6. A device for determining a geometricvehicle inclination of a motor vehicle, comprising: a speed-measurementdevice; at least one acceleration sensor; and a programmable andreadable microcontroller configured to calculate a current vehicleinclination based on a corrected acceleration value determined fromvalues of the speed-measurement device and the acceleration sensor at avehicle speed of the vehicle greater than or equal to zero andconfigured to directly transmit the vehicle inclination to at least onecontrol unit; wherein the microcontroller is configured to compare thecorrected acceleration value to a predetermined threshold accelerationvalue of the acceleration sensor and determine one of (a) an incline and(b) a decline as a function of a deviation direction.
 7. The deviceaccording to claim 6, wherein the at least one control unit includes atransmission control unit configured to process signals output by themicrocontroller.
 8. The device according to claim 6, wherein the atleast one control unit includes at least one of an engine control unit,an all-wheel-drive control unit, a brake control unit, an adaptivecruise-control unit, a vehicle-dynamics control unit and a drive-traincontrol unit, the at least one of the engine control unit, theall-wheel-drive control unit, the brake control unit, the adaptivecruise-control unit, the vehicle-dynamics control unit and thedrive-train control unit configured to process signals output by themicrocontroller.
 9. The device according to claim 6, further comprisingan instrument display configured to display the vehicle inclination. 10.The device according to claim 6, further comprising an arrangementconfigured to activate a rollover warning device in response to aspecifiable transverse inclination in accordance with the vehicleinclination determined by the microcontroller.
 11. A device fordetermining a geometric vehicle inclination of a motor vehicle,comprising: means for calculating a speed gradient from a measuredvehicle speed; means for deriving an acceleration value from a forceacting on an acceleration sensor for one of (a) a traveling vehicle and(b) a standing vehicle, the acceleration sensor configured to generatean acceleration signal; means for calculating a corrected accelerationvalue as a function of the speed gradient; means for directlycalculating a current vehicle inclination from the correctedacceleration value; means for comparing the corrected acceleration valueto a predetermined threshold acceleration value of the accelerationsensor; and means for determining one of (a) an incline and (b) adecline as a function of a deviation direction.